The present invention relates generally to a method of making a pulley from sheet metal or metal stampings, and also relates to a tool for use in making such pulley.
In the manufacture of sheet metal pulleys it is common to form at least a part thereof by a spinning process in which a spinning tool, such as a roller whose outer periphery has the configuration desired of the work piece, is forced against the rotating work piece. U.S. Pat. No. 3,633,431 which issued to Peter J. VanBussel on Jan. 11, 1972 discloses a method of making a sheet metal pulley in which a pair of metal blanks are subjected to a number of stamping operations to form a clinched assembly. As a final operation the clinched blank assembly is subjected to a spinning operation to form a V groove in the assembly. The spinning operation is performed by urging a roller with a V-shaped outer configuration between a pair of flanges to spread the flanges into the desired V shape. U.S. Pat. No. 1,680,061 which issued to R. J. Nelson on Aug. 7, 1928 and U.S. Pat. No. 2,955,748 which issued to R. J. Killian on Oct. 11, 1960 both disclose methods of making spun pulleys in which the pulley is formed completely by spinning operations. In the final operation a V groove is formed in the pulley by a spinning wheel having the desired V configuration.
The spinning operation employed in the prior art manufacturing of sheet metal pulleys has had one basic deficiency which made it difficult to control required tolerances and resulted in a high number of scrap parts. The deficiency resided in the use of the spinning wheel which is brought to bear against the rotating pulley or work piece. As the V-shaped spinning wheel progressively moved inwardly to the work piece an area or line contact between the spinning wheel and work piece along a radius of the work piece increased and this resulted in conflicting speeds at various points along the area of contact so that there was a high degree of relative sliding movement between the spinning wheel and the work piece. For example, when the spinning wheel first contacts the rotating work piece, the spinning wheel is caused to rotate at a peripheral speed corresponding to the peripheral speed of the work piece. As the spinning wheel is forced inwardly to form a groove, the tip of the spinning wheel contacts a portion of the rotating work piece having a smaller diameter than the area originally contacted. This tends to reduce the speed of rotation of the spinning wheel. However, as the spinning wheel is moved inwardly the sides of the V configuration of the spinning wheel which are on a smaller diameter than the tip of the spinning wheel contact sides of the V being formed on the work piece which are on a larger diameter of the work piece than that portion being contacted by the tip of the spinning wheel and this tends to attempt to drive the spinning wheel at a higher speed. These conflicting driving forces on the spinning wheel necessarily result in relative sliding movement between the spinning wheel and work piece, and this relative sliding movement results in galling of the work piece. The degree of galling necessarily is dependent upon the force with which the spinning wheel is forced against the work piece and the amount of relative movement between the spinning wheel and work piece.